Intravenous infusion therapy is prescribed where it is desirable to administer medications and other fluids directly into the circulatory system of a patient. Infusion pumping systems are used to pump the prescribed infusates from a bag, bottle, or syringe to the patient. For example, the infusion system of Epstein, U.S. Pat. No. 4,696,671, provides a computer-controlled infusion system using a disposable cassette and able to pump plural fluids through plural input ports and at least one patient output port simultaneously or in time sequence.
For many patients, an infusion pumping system is frequently used in conjunction with an electrocardiograph to monitor the heartbeats of the patient. The electrocardiogram (ECG) obtained comprises a number of leads, or records of potential differences, between electrodes positioned on the surface of the patient's body. Typically, a four-lead system is used to monitor the patient's condition. A twelve-lead system is used to obtain a more accurate ECG on which to base diagnoses and therapeutic prescriptions.
The ECG is a record of the electrical signals of the patient's heartbeats. An artifact in this record is undesirable because, if not detected and identified as an artifact, it may cause a physician to misinterpret the ECG. The strongest portion of the ECG is known as QRS and is the most important portion of the signal for interpreting the patient's condition. All ECG monitors filter out artifacts to some extent, and ideally the artifact will be too low to be confused with QRS. The twelve lead ECG monitors have a better capacity for filtering out artifacts of all sorts than the four-lead monitors. However, the potential for artifact occurrence still exists in all ECG systems.
Artifacts may be caused by a number of phenomena: room lights, patient movement, perspiration on the patient's skin. Artifacts have also been observed as associated with infusion pumping systems. Previously, it had been thought that pump-induced artifact was due to a piezoelectric effect of a changing strain rate in the plastic tubing inducing a miniscule electric current. It had been thought that all infusion pumps exhibited this effect, but little or no work on reducing or eliminating the effect had been accomplished.